How can the Ultra Flexible cable sold here which contains double 12AWG cable actually be rated at 40A continuous? Sounds like 32A continuous to me?
What am I missing here?
You may be missing that the paired conductors are 105C copper. Here is a link to an NEC ampacity chart.
12AWG copper rated to 90C (105C is not listed) is rated to 30A doubling the conductors would get you to 60A before de-rating 20% for 4 current carrying conductors for a total of 48A.